Many world interpretation towards building a powerful computer
Today’s blog is about a next-generation computer defined to be very powerful and capable to solve complex problems (like breaking cipher) in a matter of secs which the current supercomputers are not able to do. I am not sure how true this is that but let’s see by understanding and realising it.
In this post, we will concentrate more on the physical nature of that computer and understand what does quantum physics have to do with it which will be the source of the unlimited computing power. Quantum physics is itself very mysterious and we have only known about the weird behaviour on the subatomic level like electrons and photons.
An example
Let’s take an example of a problem where a person standing in a junction, has to decide on one path to reach his destination, only one path is correct and the rest 3 are dead-end.
In a classical computer, we would solve by going through each path, come back to start if found a dead end and then take another path, which in this case would take a maximum of 4 shots to find the correct route. But with a quantum computer, it will take only one shot to find the correct path. Even though we complicate the problem by making thousands of paths through that junction, we still can find the correct path in just one shot and of course, it's not limited to that number.
To explain better how it works I will have to take through these three basic principles of quantum physics which are the minimum theoretical requirements to build a quantum computer:
Continuum of states
A state can be defined as a specific property of any physical object/entity in space and time. A switch can be in one of the 2 states: On or off. Flipping a coin gives you one of the two states: Head or Tail.
In the above example of the person in the 4-path junction, when he moves through the space and time his state will change from 0 -> 1 or 1 -> 0 -> 2 or 2 -> 0 -> 3 and so on. This is often a general phenomenon of classical physics, whereas in a quantum world a switch can be in both the states On and Off, flipping of coin will result in both Head and Tail, and the person trying to find the correct path will be everywhere.
This term is more often refer to as “Superposition”.
In a classical computer, such states are defined in a bit (0 or 1). So, one bit can hold one of the 2 states, 2 bits can hold one of the 4 states (00, 01, 10, 11). In the case of a quantum computer, Qubit (Quantum Bit) is used where 1 qubit can hold both 2 states (0 and 1) at the same time and 2 qubits can hold all 4 states at the same time.
Pretty weird phenomenon right, which means I can be at my work and home and driving at the same time, but then in reality why can’t I experience all of them at the same time and only be available at work or home or driving? If I flip a coin, why don’t I see head and tail at the same time? I guess it’s our limitation as physical beings where we can see one thing or event at any time.
Randomness
With the above question in mind, let's try to see what is the true meaning of randomness.
In the event of flipping a coin, you throw it and saw the value, its heads in your case. This is the value you see which looks to be random but it is not truly random. If you want to predict flipping a coin brings a head or tail, you can try to measure all the initial parameters like the position of the coin itself, your body, air at the room, etc with sufficient accuracy. But in actuality, we really don’t know what causes the result to be a head or tail and looks truly random.
Does that mean randomness is some lack of information? Something seems to us random, but we believe that if we just had more information, then we could certainly predict an outcome. It is really hard to imagine the real randomness when the outcome cannot be predicted with all information available.
Now imagine in the example of the person is you and in search of the correct path, and we have four identical universes where this event takes place. In the first one, you moved from point 0 to 1 takes the upper way, and hit the dead end. While in the second universe, you took the lower way to point 3), and hit the dead end and so on for the rest two-path as well. Now, the most important part since these universes are completely identical at the start of the experiment, there are four identical you observing the result there. Does that mean you truly choose a random way whereas in actual you took all the four paths but happened in different universes?
There’s no randomness at all, but for you, subjectively, the result appears to be random. Because you cannot be in all places simultaneously. You observe the random result, but different for different you. I am not trying to convince you to accept this picture of different universes literally. But mathematically, the behaviour of the electron in its own realm works like that. In quantum mechanics, there’s no such thing as a trajectory of an electron or a photon or any other small particle. We can detect and fix the points of the electron departure and arrival here, but we can say almost nothing about what happens in between.
This true meaning of randomness gives the immense potential for parallel computing power. It's just about throwing a problem in the air and we know now there are multiple possible outcomes that we just need to know how to interpret giving us all the possible results in one shot.
Interference
If we accept that these different possibilities of an event can be implemented somewhere in a computer, the next natural question is, how we can see all the results?
“A German philosopher Immanuel Kant stated that the concept of the space is imminent to our brain, not to the real world itself, and the real world itself is maybe something very different.”
“Albert Einstein once wrote: People like us who believe in physics know that the distinction between past, present and future is only a stubbornly persistent illusion. Time, in other words, he said, is an illusion. Many physicists since have shared this view, that true reality is timeless”
“An American physicist, Hugh Everett III in 1957 proposed this new concept of a multiverse, probably an infinite stack of universes, which are in some sense parallel.”
We can imagine at the beginning of time all these universes were identical. But with the passing of time, random events occur, which divide these universes into different types depending on the results of these random events. When we observe some random event our previously identical copies in different universes start to differ and these different copies from now on can act differently. We cannot interact with each other since we are in different universes. So, there is so much available computing power in this multiverse, we are not able to use it since there’s no way we could collect the result of this distributed computation, right? Well, fortunately, sometimes we can move it, and this can be done through the process of interference.
Interference is not an act of measurement, because measurement collapses the possibilities to one reality. In simple terms when you flip the coin and hold it closed in your palm, that state is called super-position where you have the power to imagine both the universe with different results. The act of opening the palm and seeing the result collapse the possible outcome to one state. There is a scientific term to it called “Wave function collapse”.
That means the quantum computer will not try to see the result rather it will use interference to collect all the results from different universes. What is interference and how can we imagine that? A good example of interference can be seen in the below image, where when two waves collide with each other it creates an additional set of waves with different amplitudes. If the two waves have the same frequency then the collision results in constructive interference and if they are different they result in destructive interference. At any point, the interference gives us an idea to calculate the state of the two waves before the collision.
Now, what do the waves have to do with us? Well, if we see the structure of the physical universe, they are made up of atoms. Further dividing atoms give subatomic particles like electrons, photons etc and at some point further dividing the particles it's believed that we are made up of some sort of electromagnetic waves. These waves carry information that basically constructs the physical universe. This could be imagined similar to the radio waves surrounding us which carries information of TV, FM, news, mobile comms etc but the device is something that tunes with that radiofrequency and decodes the information to something meaningful like visuals or songs.
If you imagine all these infinite parallel universes at the same place around us and are vibrating at different frequencies, then the interference between these electromagnetic waves we can extract something for our distributed computation. Running different paths of computation in different universes and make them interfere, then we will be able to collect some information about the result from all these branches. This is what quantum computing is all about. Sounds simple, can we implement it?
Theoretically yes, but practically we have a problem which I think you also have imagined that. Let's say we are flipping the coin and have universe A and B where we will get to see different results. Both the universe where the event happens should be equal means A — B = 0. When the flip coin event happens and performing interference to collect results we should be able to get the result of only that flip event. But in reality, the universe is really very very big and billions of random events are happening every second and the waves of those random events can interfere with the coin flip event adding errors to the collected results. To have the desired result there are few things which are been done to reduce the errors:
- Make the computation very fast to eliminate the probability of another random event in the environment.
- Reduce the temperature of the surrounding environment which slows down the random event and gives time while reading interference. That's why you will see the quantum computers kept at -200 degrees Celcius.
- Try to isolate the computing system as much as possible which could be the hardest thing to do.
I guess research is in progress to find the best and effective approach to collect the result from the multiverse. I know it's a long way to go, but at least with this post, I wanted to give some basic understanding which probably tries to open our minds to think in a very different way. Just closing my thought with this quote from Mark Helprin, Winter Tales “If nothing is random, and everything is predetermined, how can there be free will? The answer to that is simple. Nothing is predetermined; it is determined, or was determined, or will be determined.”
Originally published at https://www.tech-quantum.com on September 5, 2021.
